A lot of sliding load members, such as the flaps and slats used during takeoff and landing, are employed in wings and the like of aircraft as illustrated in FIG. 5(a). They are required to have exceptionally high reliability in view of the fact that they are being used in an aircraft. Iron steel materials have conventionally been used as various wear resistant members, mainly because their inexpensive price and excellent workability enable manufacture of products with an intricate design at a low cost. In recent years, however, titanium has come to be used for sliding members to meet the needs for further reduction in weight. Owing to the excellent specific strength of titanium, the weight of members can be reduced. However, because they have an inferior wear resistance and sliding property, titanium members require an improvement of the wear resistance and sliding property by use of a surface coating such as Cr plating or WC—Co sprayed coating. In addition, plasma carburization has recently been developed (JP-A 2002-371348).
Although Cr-plated or WC—Co sprayed Ti materials have high wear resistance, they are inferior in fatigue strength to unprocessed Ti materials. Further, peeling of the coating inevitably occurs when a coating a substance is different from that of the base material is attached to the outer surface of the base material. On the other hand, plasma carburization has the problem that in spite of having an excellent sliding property as well as excellent wear resistance, it greatly reduces the fatigue strength of Ti materials.
Titanium materials are used as members for aircraft for which fatigue strength is needed. However, surface processing reduces their fatigue strength, which poses a serious problem. There is accordingly an eager demand for the development of a surface processing method for obtaining a titanium material having improved wear resistance and sliding property and moreover having improved fatigue strength.